US3930134A

US3930134A - Pneumatic power-unit having a driving piston and an exhaust valve

Info

Publication number: US3930134A
Authority: US
Inventors: Joseph R Rostron; Lawrence A Brunson; Otto H Soles
Original assignee: Westinghouse Electric Corp
Current assignee: ABB Inc USA
Priority date: 1973-09-27
Filing date: 1973-09-27
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30
Also published as: FR2246051A1; JPS5060773A; CA1019370A; DE2445671A1

Abstract

An improved pneumatic power unit is provided including a penumatic piston reciprocally operable within an operating cylinder housing, which, in one conceivable application, operates the contact structure of a power circuit-breaker, and uses a normally-open three-way valve, which normally provides highpressure gas on both sides of the driving piston within the operating cylinder housing. During the closing operation of the circuit-breaker, when the pneumatic power unit of the instant invention is applied to this particular application, the threeway normally-open valve is operated to exhaust one side of the driving piston, and the high-pressure gas already present on the other side of the piston provides the required closing force to close the contacts of the circuit-breaker against the usuallyprovided accelerating spring pressure tending to open the breaker. The de-energization of the normally-open three-way valve returns the closing or driving piston to its normal reset position, in such a particular application, thus not requiring a return spring, since the cross-sectional area of the piston-shaft is acted upon by the internal high-pressure gas present on the return or non-working side of the piston assembly in the cylinder housing, and since normal atmospheric air pressure obviously exists on the outside or externally of the operating-cylinder housing thereby exerting relatively little inward force on the cross-sectional area of the piston rod.

Description

United States Patent 'Rostron et al.

[ Dec. 30, 1975 Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Sept. 27, 1973 [2]] Appl. N0.: 401,520

[52] US. Cl. 200/82 B; 200/83 A; 200/148 F; 91/416; 137/625.64 [51] Int. Cl. H0111 35/38 [58] Field of Search 335/174, 191; 200/82 R, 200/82 B, 82 C, 169 R,145, 153 G, 153 V, 153 H, 148 E, 148 F, 83 A, 83 C, 83 J; 137/625.64; 91/416 [56] References Cited UNITED STATES PATENTS 2,667,554 l/l954 Shores 200/148 F 3,334,202 8/1967 Tognella... 200/153 H 3,438,246 4/1969 Lotti 200/82 R 3,591,051 7/1971 Mitchell 200/83 A 3,624,329 11/1971 Fischer 200/148 F 3,646,292 2/1972 Barkan 200/82 B 3,766,536 10/1973 Hile 200/83 A 3,766,834 10/1973 Kraemer 200/83 C 3,780,528 12/1973 Brandenburg... 200/83 A FOREIGN PATENTS OR APPLICATIONS 915,858 1/1963 United Kingdom I? E 23 N as "Q 65 N;

4o 4 2 nnna 32 l l Primary Examiner-Gerald P. Tolin Attorney, Agent, or FirmW. R. Crout [57] ABSTRACT An improved pneumatic power unit is provided including a penumatic piston reciprocally operable within an operating cylinder housing, which, in one 'conceivable application, operates the contact structure of a power circuit-breaker, and uses a normallyopen three-way valve, which normally provides highpressure gas on both sides of the driving piston within the operating cylinder housing. During the closing operation of the circuit-breaker, when the pneumatic power unit of the instant invention is applied to this particular application, the three-way normally-open valve is operated to exhaust one side of the driving piston, and the high-pressure gas already present on the other side of the piston provides the required closing force to close the contacts of the circuit-breaker against the usually-provided accelerating spring pressure tending to open the breaker.

16 Claims, 4 Drawing Figures CLOSED POSITION OF BKR, PISTON RESET US. Patent Dec. 30, 1975 Sheet10f3 3,930,134

w 0N m U.S. Patsnt Dec. 30, 1975 Sheet 2 of3 3,930,134

ZOELmOQ ZmEO omanzwtl U.S. Patent Dec.30, 1975 Sheet3of3 3,930,134

CROSS-REFERENCES TO RELATED APPLICATIONS Applicants are not aware of any related patent applications pertinent to the present invention.

BACKGROUND OF THE INVENTION In U.S. Pat. No. 3,624,329, issued Nov. 30, 1971 to William H. Fischer et al, and assigned to the assignee of the instant application, there is illustrated and described a pneumatic operating mechanism for a circuitinterrupter in which a spring-retrieved closing piston is pneumatically operated to rotate a circuit-breaker closing lever and thereby to close the breaker contacts. Upon the removal of pressure from the closing piston, a compression Spring, located within the operating cylinder, retrieved the closing or driving piston to thereby disengage the piston-rod from a roller associated with the rotatable operating lever. The closing piston utilized a normally-closed three-way valve, and the valve provided the piston with low pressure on the working side of the closing piston in its reset position. The working side of the piston was pressurized by operation of the three-way valve to provide the requisite closing force on the piston to close the breaker. In addition, there was a compression spring provided in the closing cylinder on the non-working side of the piston to return the piston to its reset position, so that the piston did not interfere with the tripping operation of the breaker after a closing operation had been accomplished. Also, a latch-check switch de-energized the solenoid valve after the mechanism was completely closed, and, in addition, a switch was required to prevent tripping of the circuit-breaker until the driving piston had been returned to its original reset position.

The present invention is particularly concerned with an improved pneumatic power unit having wide application, with one particular application concerned with a circuit-breaker operating mechanism operable to effect the closing operation of a power circuit-breaker against heavy accelerating opening spring pressures tending to open the breaker contacts, and yet having the piston in a position out of the way during a subsequent tripping operation in the normal latched-closed position of the breaker. The invention is particularly suitable for the operating mechanisms of power circuitbreakers of relatively high-voltage and high-current carrying capacity.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided an improved pneumatic power unit having wide application, one particular application being its use with an operating mechanism assembly operable to close the circuit-breaker contacts of a power circuitbreaker by piston action, which involves a normallyopen three-way control valve which exhausts one side of the driving piston to provide the power-closing stroke for the mechanism.

To effect a retrieving action of the piston, the threeway control valve is de-activated or de-energized, and thus provides high pressure on both sides of the driving piston. Due to the differential pressure acting across the cross-sectional area of the piston-shaft extending out of the operating cylinder, with high-pressure gas 2 existing on the non-working side of the piston, and normal atmospheric air pressure existing on the outside of the piston-operating cylinder, there is provided the requisite differential pressure force across the pistonrod cross-sectional area to effect the return of the piston to its normal de-activated reset position with pressure existing on both sides of the driving piston. At this time, the normally-open three-way control valve is in its de-energized position.

Further advantages will be apparent upon reading the following specification taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view illustrating the improved pneumatic power unit of the circuit-breaker in the contact-closed position with the piston assembly in its retrieved reset position;

FIG. 2 is a view similar to that of FIG. 1, but illustrating the circuit-breaker in its tripped open position;

FIG. 3 illustrates the position of the several parts during a power-closing stroke of the circuit-breaker mechanism; and,

FIG. 4 is an end sectional view taken substantially along the line IVIV of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, and more particularly to FIG. 1, it will be observed that there is provided an operating mechanism, generally designated by the reference numeral 1, operable to effect the closing and opening operations of the circuit-breaker contacts 2, 3 and 4 of a power circuit-breaker 5. The three sets of circuit-breaker contacts 2, 3 and 4 are diagrammatically illustrated in FIG. 1, inasmuch as the present invention is particularly concerned with the circuitbreaker operating mechanism 1. The particular operating mechanism 1 is associated, for example, with a power circuit-breaker 5 of the type set forth in U.S. Pat. No. 3,624,329, issued Nov. 30, 1971, to William H. Fischer et al, and assigned to the assignee of the instant application. Although the view in FIG. 1 shows a direct mechanical connection to the contacts, the mechanism may alternatively operate control valves, the latter in turn controlling gas flow to pistons which are linked to the contacts as in U.S. Pat. No. 3,624,329. Reference may be made to this patent for background information regarding certain structural component parts of the power circuit-breaker, if desired. Since the present invention is particularly concerned with the operating mechanism 1, however, the contact structure has been simplified, and is, as shown, diagrammatically illustrated in FIG. 1 of the drawings.

A trip-magnet assembly 7 is provided for releasably magnetically latching the circuit-breaker 5 in the closed position. As set forth in the aforesaid patent, generally, the trip-magnet assembly 7 comprises a holding-magnet 11 and a trip-lever l3, pivotally mounted upon a stationary pivot 15, and having its tail portion 17 maintain a toggle-linkage 19 in a slightly underset condition. As shown in FIG. 1, the toggle-linkage 19 comprises a pair of toggle-

links

21, 23 one toggle link 21 being pivotally mounted upon a stationary pivot 25, and the other toggle link 23 being pivotally connected to a moving pivot 27 at the outer free end of a main operating lever assembly, generally designated by the reference numeral 29, and pivotally mounted upon a 3 stationary pivot 30.

An operating rod 31 is pivotally connected intermediate the ends of the main operating lever-assembly, as at 32, and is also connected to the movable contacts 2a, 3a, 4a of the circuit-breaker 5, diagrammatically illustrated, which are under heavy spring pressure 34 in the closed-circuit position of the interrupter tending to effect their opening operation, as shown in FIG. 1. In more detail one or more accelerating springs 34 are interposed between a stationary cross-plate 36 extending across and affixed, as by welding, for example, to two heavy side support plates 38, which journal the various

stationary pivot pins

25, 30, and 37 of the mechanism 1. The other end of the compression spring 34 bears upon a movable spring-plate 40 affixed to and movable with the contact operating rod 31.

A pair of

bumpter assemblies

42 and 43 are provided to cushion the ends of the opening and closing movements of the main operating lever-assembly 29; and an auxiliary switch assembly 44 is provided, being connected through a bell-crank lever 46 and a link 48 to a portion 50 of the main operating lever-assembly 29 to provide the desired actuation of the auxiliary switch 44. As well known by those skilled in the art, the auxiliary switch 44 controls electrical circuits (not shown), which are responsive to the open and closed-circuit positions of the interrupter 5.

As illustrated in FIG. 1, the main operating leverassembly 29 is under spring pressure 34 to open the contacts 2, 3 4, but is maintained in its closed position, as shown in FIG. 1, under such spring pressure 34 by the latching action of the trip-magnet assembly 7.

Trip coils

52, 53 are associated with the magnet assembly 7, and when energized, divert the magnetic flux within the holding magnet 11 and thereby effect the release of the armature, or keeper 55, which in turn, will permit collapse of the toggle-linkage l9 and thereby allow springopening operation of the contacts 2a, 3a, 4a of the cirucit-breaker 5.

To effect the closing operation of the circuit-breaker 5, there is provided an improved closing-piston assembly 57, including a driving piston 59 reciprocally operable interiorly of a pneumatic operating cylinder 60 normally having high-pressure air, or gas 61 on both sides thereof. The fluid 61 may, of course, be other than air, and, in fact, may be any suitable gas, even a gas suitable for arc-extinguishing purposes in the breaker 5. This is particularly true where the circuitbreaker is one of the sulfurhexafluoride (SF type, in which it is not desired to utilize two separate gases, such as SF gas and compressed air, in the same breaker installation 5. Thus, the sulfurhexafluoride gas 61 may not only be used for arc-extinguishing purposes at the contacts 2, 3, 4, but in fact is used for the pneumatic operation of the driving piston-assembly 57.

It will be observed that the driving piston 59 is interconnected with a piston rod 63, which has an actuatingend portion 65 with a longitudinal slot 67 provided therein. This provides a lost-motion connection 64 between the rod 63 and the roller 68 carried by the lever 29. When the circuit-breaker 5 is in the opencircuit position, as illustrated in FIG. 2, it will be observed that the roller 68, movable with the main operating lever assembly 29, is in a position close to the end 67a of the elongated slot 67. In this event, exhausting of gas 61 from the righthand end 71 of the piston cylinder 60 will permit the high-pressure gas 61 on the left-hand working face 73 of the drivinging piston 59 to effect a rightward closing operation of the driving piston 59, and thereby forcibly carry the roller 68 and hence the main operating lever-assembly 29, in a clockwise direction, as viewed in FIGS. 2 and 3, to thereby effect a closing operation of the interrupter 5. FIG. 3 shows such a power-closing operation of the circuit breaker 5 in a more detailed manner.

The present invention is suitable for use with any conventional, normally-open, three-way control valve 75, which when operated, will exhaust the region 71 on the right-hand non-working face of the driving piston 59. Deenergization of the normally-open three-way control valve 75, high-pressure gas 61 is again permitted to flow through the piping 77, 78 and into the righthand chamber 71 of the operating cylinder 60 and the consequent equalization of gas pressure on both sides of the piston 59 will drive the piston assembly 59 to its leftward end reset position, as shown in FIG. 1, by virtue of the differential pressure existing on the piston assembly 59. As well known by those skilled in the art, this differential pressure exists because of the crosssectional area A (FIG. 4) of the piston-rod 63 itself. Thus, with reference to the cross-sectional area A (FIG. 4) of the piston-rod 63, it will be observed that there is high-pressure gas 61 acting to force the pistonrod 63 leftwardly out of the operating cylinder 60, as viewed in FIG. 1, whereas there is merely atmospheric pressure, or low-pressure gas, externally of the operating cylinder 60. An unbalanced pressure force upon the piston rod 63 of the piston-assembly 59 consequently exists.

The equalization of gas pressure on both sides of the piston 59 will, as mentioned, force the piston 59 to the left to be ultimately arrested at an annular stop designated by the reference numeral 72.

High-pressure gas 61 is constantly supplied to the operating cylinder space 76 by a high-pressure supply pipe 81 fed from a suitable high-pressure reservoir 85.

To prevent leakage of gas 61 out of the pneumatic operating cylinder 60, there is provided a syIphon-bellows 80, for example, to prevent leakage of gas along the opening 82 provided in the end plate 84 of the operating cylinder 60. The present invention, of course, is not limited to the use of a sylphon-bellows 80, but any good seal may be provided, as desired. The use of a sylphon-bellows 80, of course, assures that long operational life will be obtained with no leakage occurring along the opening 82 in the end head-plate 84 of the operating cylinder 60.

The electrical control 86 for the actuation of the three-way pneumatic control valve is illustrated in FIG. 1, and it will be observed that upon pressing or closing the close button 88, the control valve 75 will be actuated, and will thereby exhaust the region 71 on the right-hand non-working face 90 of the driving piston 59. This will, of course, permit the normally-present high-pressure gas 61 in the region 76 on the lefthand working face 73 of the driving piston 59 to drive the piston-rod 63 to the right, and thereby effect closing of the circuit breaker 5. The closed position of the contacts 2, 3, 4 of the circuitbreaker 5, of course, is resisted by accelerating springs 34 normally provided in circuit-breaker structures to assist in a subsequent quick-opening operation of the contacts.

From the foregoing description, it will be apparent that there has been provided an improved closing-piston assembly 57 for a circuit-breaker mechanism 1, which utilizes a normally-open three-way valve 75. The

normally-open three-way valve 75 provides high-pressure gas on both sides of the driving piston 59. The valve 75 exhausts one side 71 of the driving piston 59, and the high-pressure gas 61 on the other side 76 of the driving piston 59 provides the required closing force to close the breaker. The return of the drivng piston 59 to its normal reset position, as shown in FIG. 1, does not require a spring. As mentioned, the area A (FIG. 4) of the piston-shaft 63 with high-pressure gas existing on the inside of the piston assembly 61 in the region 71, and normal atmospheric air pressure existing on the outside of the operating cylinder 60, provides the re quired force to return the driving piston 59 to its end leftward reset position, as shown in FIGS. 1 and 2.

The valving arrangement is calculated and has been observed to be very consistent in its operation over a wide range of pressures. This consistency allows the usual latch-check switch to be deleted, and the valve to be deenergized by the auxiliary contacts that are required for other functions as well. The switch formerly used to assure that the driving piston 59 is fully returned prior to a trip operation is also eliminated, due

to the consistency of operation of the mechanism 1.

The full return stroke of the driving piston 59 prior to a trip operation can be assured without the use of this switch.

Although there has been illustrated and described a specific structure, it is to be clearly understood that the same was merely for the purpose -of. illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

We claim:

1. An operating mechanism for a circuit-interrupter including in combination:

a. means defining separable contact means;

b. a movable member;

c. means rendering opening and closing motions of said separable contact means responsive to the movement of said movable member (29);

d. a pneumatic operator including a driving-piston operable within a pneumatic operating cylinder and having a piston-rod extending externally out of said pneumatic operating cylinder;

e. said piston rod being connected with said movable member (29) to cause the actuation thereof;

f. said piston-rod extending only out of one end of the operating cylinder on one working side of the driving piston;

g. the other end of the operating cylinder on the nonworking side of the piston being closed with respect to the piston-rod;

h. valve means normally maintaining high-pressure gas within said pneumatic operating cylinder on both the driving and non-driving sides of the driving-piston to thereby extend the piston-rod outwardly by differential piston action; and,

. means for operating said valve means and exhausting gas from the non-driving side of the driving-piston at said other end of the cylinder to thereby move the driving-piston toward the closed end of the operating cylinder and the movable member (29) to close the breaker contacts.

2. The combination according to claim 1, wherein the movable member is a rotatable main operating lever pivotally mounted upon a stationary pivot and connected to said piston-rod.

3. The combination according to claim 2, wherein the connection between the piston-rod and the rotatable main operating lever is a lost-motion connection, whereby the driving-piston may assume its reset position without interference with the rotatable main operating lever.

4. The combination according to claim 1, wherein a collapsible toggle-linkage releasably maintains the movable member in its closed position.

5. The combination according to claim 4, wherein a holding means including a magnetically-actuated trigger-arm maintains the collapsible toggle-linkage in an underset condition.

6. The combination according to claim 1, wherein opening accelerating spring means tends to bias the movable contacts of the circuit-interrupter in the opening direction, and a lost-motion connection is provided between the movable member and the piston-rod of the pneumatic operator.

7. The combination according to claim 1, wherein the valve means includes a normally-open three-way control valve, and the movable member comprises a rotatable operating lever pivotally mounted upon a stationary pivot and having a lost-motion connection with the piston-rod ofthe pneumatic operator.

8. The combination according to claim 3, wherein the lost-motion connection is an elongated slot provided in the piston-rod.

9. The combination according to claim 1, wherein the normal reset position of the driving-piston with high-pressure gas existing on both sides thereof is intermediate the ends of the pneumatic operating cylinder and against a stop portion provided on the pneumatic operating cylinder.

10. A pneumatic power-unit including, in combination:

a. means defining an operating cylinder;

b. a driving piston operable within said operating cylinder and responsive to the gas-pressure conditions existing therewithin;

c. a piston-rod fixedly secured to and movable with said driving piston and responsive to the movement thereof;

d. said piston-rod projecting externally of said operating cylinder at one end thereof through a first open cylinder-head and having an effective crosssectional area of A;

. a first pneumatic region (76) defined by said driving piston, the inner side walls of the operating cylinder and said first open cylinder-head of the operating cylinder at said one end of the operating cylinder;

f. a second pneumatic region (61) disposed on the other side of said operating piston from said first pneumatic region;

g. high-pressure gas conditions existing in said first pneumatic region at all times during operation of the pneumatic power unit;

h. operating means including a three-way control valve for alternately pressurizing or exhausting said second pneumatic region;

i. the pressurization level of said second pneumatic region being substantially at the same gas-pressure level as said constant-pressure gas-level of the first pneumatic region; and,

j. the cross-sectional area A of said piston-rod being of sufficient adequate cross-sectional area to rapidly retract, by differential piston action, the

operating movement of the operating piston toward said one end of the operating cylinder, whereby pressurization of the second pneumatic region will operatively move the piston-rod toward said first open cylinder-head of the operating cylinder, and exhausting of the second pneumatic region by operation of said control-valve will correspondingly effect driving inward motion of the operating piston and the piston-rod toward the other or closed second cylinder-head for retracting purposes of the operating piston.

11. The combination of claim 10, wherein stop means for the operating piston is provided along the inner side wall of the operating cylinder.

12. The combination in a circuit-breaker of separable contacts separable to establish arcing, means biasing said separable contacts to the open-circuit position, a closing mechanism for effecting the closing of said separable contacts including a pneumatic operator, said pneumatic operator including a driving-piston operable within a pneumatic operating cylinder, a rotatable main lever pivotally mounted upon a stationary pivot, a piston-rod connected to said driving-piston and having a lost-motion mechanical connection with said rotatable main lever, said piston-rod projecting externally of said operating cylinder at one end thereof through a first open cylinder-head and having an effective cross-sectional area of A, a first pneumatic region (76) defined by said driving-piston, the inner sidewalls of the operating cylinder and said first open cylinder-head of the operating cylinder at said one end of the operating cylinder, a second pneumatic region (61) disposed on the other side of said operating piston from said first pneumatic region, high-pressure gas conditions existing in said first pneumatic region at all times during operation of the pneumatic operator, operating means including a three-way control-valve for alternately pressurizing or exhausting said second pneumatic region, the pressurization level of said second pneumatic region being substantially at the same gaspressure level as-said constant-pressure gas-level of the first pneumatic region, the cross-sectional area A of said piston-rod being of sufficient adequate cross-sectional area to rapidly retract by differential pressureaction the operating movement of the operating piston toward said one end of the operating cylinder, whereby pressurization of the second pneumatic region will operatively move the piston-rod toward said first open cylinder-head of the operating cylinder, and exhausting of the second pneumatic region by operation of said three-way control-valve will correspondingly effect inward driving motion of the operating piston and the piston rod toward the other or closed second cylinderhead for retracting purposes of the driving-piston, and said retracting movement of the driving-piston and said lost-motion connection will locate the piston-rod in a non-interfering position relevant to the rotatable main lever.

13. The combination according to claim 12, wherein the valve means comprises a three-way pneumatic control valve, said rotatable main lever is releasably maintained in its closed position by a collapsible toggle-linkage, and said collapsible toggle-linkage is maintained in an underset condition by a releasable holding means.

14. The combination according to claim 12, wherein the valve means comprises a three-way pneumatic control valve, said rotatable main lever is releasably maintained in its closed position by a collapsible togglelinkage, and said collapsible toggle-linkage is maintained in an underset condition by a releasable holding means.

15. The combination according to claim 14, wherein the releasable holding means comprises a magneticallyactuated trigger-arm.

16. The combination according to claim 15, wherein a pair of shock-absorbers cushion the opening and closing motions of the rotatable main operating lever.

Claims

1. An operating mechanism for a circuit-interrupter including in combination: a. means defining separable contact means; b. a movable member; c. means rendering opening and closing motions of said separable contact means responsive to the movement of said movable member (29); d. a pneumatic operator including a driving-piston operable within a pneumatic operating cylinder and having a piston-rod extending externally out of said pneumatic operating cylinder; e. said piston rod being connected with said movable member (29) to cause the actuation thereof; f. said piston-rod extending only out of one end of the operating cylinder on one working side of the driving piston; g. the other end of the operating cylinder on the nonworking side of the piston being closed with respect to the piston-rod; h. valve means normally maintaining high-pressure gas within said pneumatic operating cylinder on both the driving and nondriving sides of the driving-piston to thereby extend the piston-rod outwardly by differential piston action; and, i. means for operating said valve means and exhausting gas from the non-driving side of the driving-piston at said other end of the cylinder to thereby move the driving-piston toward the closed end of the operating cylinder and the movable member (29) to close the breaker contacts.

7. The combination according to claim 1, wherein the valve means includes a normally-open three-way control valve, and the movable member comprises a rotatable operating lever pivotally mounted upon a stationary pivot and having a lost-motion connection with the piston-rod of the pneumatic operator.

10. A pneumatic power-unit including, in combination: a. means defining an operating cylinder; b. a driving piston operable within said operating cylinder and responsive to the gas-pressure conditions existing therewithin; c. a piston-rod fixedly secured to and movable with said driving piston and responsive to the movement thereof; d. said piston-rod projecting externally of said operating cylinder at one end thereof through a first open cylinder-head and having an effective cross-sectional area of ''''A''''; e. a first pneumatic region (76) defined by said driving piston, the inner side walls of the operating cylinder and said first open cylinder-head of the operating cylinder at said one end of the operating cylinder; f. a second pneumatic region (61) disposed on the other side of said operating piston from said first pneumatic region; g. high-pressure gas conditions existing in said first pneumatic region at all times during operation of the pneumatic power unit; h. operating means including a three-way control valve for alternately pressurizing or exhausting said second pneumatic region; i. the pressurization level of said second pneumatic region being substantially at the same gas-pressure level as said constant-pressure gas-level of the first pneumatic region; and, j. the cross-sectional area ''''A'''' of said piston-rod being of sufficient adequate cross-sectional area to rapidly retract, by differential piston action, the operating movement of the operating piston toward said one end of the operating cylinder, whereby pressurization of the second pneumatic region will operatively move the piston-rod toward said first open cylinder-head of the operating cylinder, and exhausting of the second pneumatic region by operation of said control-valve will correspondingly effect driving inward motion of the operating piston and the piston-rod toward the other or closed second cylinder-head for retracting purposes of the operating piston.

12. The combination in a circuit-breaker of separable contacts separable to establish arcing, means biasing said separable contacts to the open-circuit position, a closing mechanism for effecting the closing of said separable contacts including a pneumatic operator, said pneumatic operator including a driving-piston operable within a pneumatic operating cylinder, a rotatable main lever pivotally mounted upon a stationary pivot, a piston-rod connected to said driving-piston and having a lost-motion mechanical connection with said rotatable main lever, said piston-rod projecting externally of said operating cylinder at one end thereof through a first open cylinder-head and having an effective cross-sectional area of ''''A'''', a first pneumatic region (76) defined by said driving-piston, the inner side-walls of the operating cylinder and said first open cylinder-head of the operating cylinder at said one end of the operating cylinder, a second pneumatic region (61) disposed on the other side of said operating piston from said first pneumatic region, high-pressure gas conditions existing in said first pneumatic region at all times during operation of the pneumatic operator, operating means including a three-way control-valve for alternately pressurizing or exhausting said second pneumatic region, the pressurization level of said second pneumatic region being substantially at the same gas-pressure level as said constant-pressure gas-level of the first pneumatic region, the cross-sectional area ''''A'''' of said piston-rod being of sufficient adequate cross-sectional area to rapidly retract by differential pressure-action the operating movement of the operating piston toward said one end of the operating cylinder, whereby pressurization of the second pneumatic region will operatively move the piston-rod toward said first open cylinder-head of the operating cylinder, and exhausting of the second pneumatic region by operation of said three-way control-valve will correspondingly effect inward driving motion of the operating piston and the piston rod toward the other or closed second cylinder-head for retracting purposes of the driving-piston, and said retracting movement of the driving-piston and said lost-motion connection will locate the piston-rod in a non-interfering position relevant to the rotatable main lever.

14. The combination according to claim 12, wherein the valve means coomprises a three-way pneumatic control valve, said rotatable main lever is releasably maintained in its closed position by a collapsible toggle-linkage, and said collapsible toggle-linkage is maintained in an underset condition by a releasable holding means.

15. The combination according to claim 14, wherein the releasable holding means comprises a magnetically-actuated trigger-arm.